The present invention relates to a spindle motor for rotatably driving an optical disk, magneto-optical disk or the like, and a disk drive unit comprising the spindle motor and an optical head.
Known disk drive units comprising a head mechanism for reading information recorded in a disk or writing information to a disk include such optical disk and magneto-optical disk drive units as CD, DVD, and MD disk drives.
For such disk drive unit, an outer rotor type brushless motor is employed as a spindle motor for rotatably driving a disk. A rotating shaft of the spindle motor comprises a turntable on which a disk is placed, and is rotatably supported by a stator using a bearing.
A sintered oil-impregnated metal bearing is generally used as the bearing. This is because such a bearing is less expensive than a roller bearing and thus can reduce the costs of a motor and device. However, unlike a roller bearing, clearance is required between a metal bearing and rotating shaft, and due to this clearance, axial run-out of the rotating shaft becomes larger than that with a roller bearing.
This axial run-out of the rotating shaft becomes surface run-out of a disk surface or axial run-out of a disk when a disk is mounted on a turntable and rotatably driven, causing such disadvantages as an optical head being unable to accurately read information from a disk or accurately write information to a disk.
Various constitutions and methods have been proposed as means for preventing axial run-out of a rotating shaft as above. In particular, the present applicant has filed applications, as in Laid-open Japanese Patent No. 2004-7905, wherein a constant force is exerted on a rotor, not only in the rotating shaft direction (the thrust direction), but also in a radial direction using a magnetic force, causing the rotor to be slightly inclined and eccentric in a prescribed direction.
By thus applying a force to a rotor in a prescribed direction, and causing the spindle motor to rotate in a state where the rotor is eccentric in a prescribed direction, axial run-out of a rotating shaft is inhibited and surface run-out and axial run-out of a disk are improved.
On the other hand, in the relative movement of a read head and disk in a disk drive, it is relatively easy for the head mechanism to track disk run-out in the focus direction, and thus signals can be read even with a certain degree of disk run-out. However, in the tracking direction, even though it is possible for the head to follow the disk run-out, greater precision in terms of surface run-out and axial run-out is demanded when compared to the focus direction.
For this reason, a technology is disclosed in Laid-open Japanese Patent No. H09-74705, wherein read head moving direction is correlated with the direction of eccentricity of a spindle motor rotor.
As suggested in Laid-open Japanese Patent No. 2004-7905, with a disk drive unit configured such that a rotor is made eccentric using a magnetic generator disposed on the rotor and a magnetic attractor covering a bearing end on the stator side, because an attractive force is exerted near the rotating shaft, obtaining sufficient eccentric action is difficult unless this attractive force is strong.
Further, as shown in Laid-open Japanese Patent No. H09-74705, for a disk drive using an optical read head, a constitution wherein a rotor is eccentric in a head moving direction is considered effective. In such a constitution, a prescribed section of a magnetic plate shaped stator core comprising a plurality of stacked magnetic plates is cut away, thereby creating magnetic unbalance with respect to a drive magnet provided on a rotor, thus causing the rotor to be eccentric in a certain direction.
Such a constitution requires not only the processing of each magnetic plate into a prescribed form, but also the assembly of the processed magnetic plates in a set combination. Further, because assembling a stator core as a drive device requires that the assembling direction be determined, such assembly is extremely troublesome.
Further, because a specialized motor is required for such a disk drive, the use of such motor is also limited.
It is therefore an object of the present invention to provide a versatile spindle motor and a disk drive unit using the motor while using a simple constitution to efficiently make a rotor eccentric.